Pritzel, Christian
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Pritzel, Christian
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Publication Access status: Metadata only , Cement hydration kinetics followed by electron spin resonanceCement hydration is driven by a complex system of chemical reactions of several hydraulic binders and water that influence each other. Here we establish a method to measure the hydration kinetics of an individual clinker phase by electron spin resonance spectroscopy. The hydration of a Mn(II) doped crystalline phase can be analyzed from the decay of signals coming from the starting material and the formed product. Transformation times can be determined by modeling the time series of the signal intensities. The host of the dopant could be identified by combining evidence from different analytical techniques including diffraction and electron microscopy. The results about the reaction kinetics are compared to those obtained from caloric measurements. The method opens a way to study the hydration of different hydraulic binders in complex systems selectively, which includes the determination of induction periods and transformation times from in-situ measurements.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Der Einfluss der Morphologie der Impfkristalle auf die Hydratation von HalbhydratDer am häufigsten eingesetzte Beschleuniger für Halbhydrat sind Gipsimpfkristalle. In wieweit die Art dieser Kristalle (Morphologie und Größe) einen Einfluss auf die technischen Eigenschaften des entstehenden Gipssteins hat ist bislang nicht ausreichend geklärt. Daher wurde in der vorliegenden Arbeit der Einfluss verschiedener Impfkristalle, deren Morphologie durch Zusatzmittel beeinflusst wurde, untersucht. Impfkristalle auch in kleinen Mengen wirken beschleunigend, Neben den Impfkristallen kommt es während der Halbhydrat‐Hydratation zur Neubildung von Dihydratkristallen. Es konnte gezeigt werden, dass Impfkristalle in der vorgegebenen Morphologie weiterwachsen. Neu gebildete Kristalle sind nicht davon betroffen. Damit lassen sich ggf. Gefüge aus verschiedenen Kristallmorphologien einstellen.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Der Einfluss von Zusatzmitteln auf das Recycling von calciumsulfat‐basierten Bindemitteln Teil II (Ausgangsstoff technischer Gips)Recycling von Gips ist ein Vorgang, der immer mehr in den Fokus der Wissenschaft rückt. Bisher liegt der Fokus jedoch im Wesentlichen auf der Entfernung von Fasern und anderen Verunreinigungen, wie z.B. Papier aus dem Recyclingmaterial. In diesem Beitrag soll untersucht werden inwiefern häufig verwendete ADDitive die Eigenschaften des Recyclingmaterials beeinflussen. Nachdem an einzelnen Kristallen bereits gezeigt wurde, dass einige ADDitive im Recyclingmaterial verbleiben, soll nun anhand von technischen Gipsproben gezeigt werden, wie diese ADDitive die technischen Eigenschaften des aus dem Recyclingmaterial hergestellten Gipses verändern. Es konnte gezeigt werden, dass die ADDitive einen wesentlichen Einfluss auf das neue Material haben, aber auch durch das Recycling ohne ADDitive werden das neue Rohmaterial und der abgebundenen Gips wesentlich beeinflusst. Insbesondere die Oberfläche des aus dem Recyclinggips hergestellten Halbhydrats verändert sich deutlich, wodurch der Wasseranspruch und verschiedene technische Eigenschaften verändert werden.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Der Einfluss von Zusatzmitteln auf das Recycling von calciumsulfatbasierten Bindemitteln Teil I (Ausgangsstoff gezüchtete Kristalle)Durch die Energiewende in Deutschland werden die verschiedenen Kraftwerksnebenprodukte, unter anderem REA‐Gips, mehr und mehr verschwinden. Aus diesem Grunde rückt das Recycling von Gips zunehmend in den Fokus der Wissenschaft. Bisher wurde der Einfluss von ADDitiven auf das Recycling von Gips nur begrenzt untersucht. Mit den vorgestellten Untersuchungen soll ein Beitrag zu dieser Diskussion geliefert werden. Dazu wurden Gipskristalle auch in Anwesenheit von ADDitiven per Diffusionsynthese aus Natriumsulfat und Calciumchlorid hergestellt. Diese wurden anschließend zu Halbhydrat umgesetzt und dieses wieder hydratisiert. Beide Vorgänge wurden mit verschiedenen Methoden untersucht. Mit Hilfe der Elektronenmikroskopie konnten die Morphologien sowohl der Gipskristalle als auch des gebildeten Halbhydrates bestimmt werden. Die Wärmeflusskalorimetrie hat dazu beigetragen den Hydratationsverlauf des Halbhydrates zu verfolgen. Es konnte gezeigt werden, dass einige ADDitive im System verbleiben und im Recyclingprodukt zu neuen Herausforderungen führen können.Source Type:Article5 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Improved flexural strength and morphology of gypsum by wollastoniteThe role of β‐wollastonite on the flexural strength of gypsum obtained from the hydration of alpha‐hemihydrate was investigated in this work. Starting with a synthesized Xonotlite obtained from the industry, dehydration was carried out at 880°C giving rise to the β‐wollastonite which was identified by X‐ray diffraction. The pure gypsum samples were prepared and compared with 3% and 5% replacements of the wollastonite. Increased flexural strengths were observed for 2, 7 and 28 days of storage in room temperature, normal water, and cold water. It was remarkable that the strength in water storage increased. The crystal morphology of the obtained gypsum was also improved in the presence of β‐wollastonite.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Influence of iron doped TiO<sub>2</sub> nanotubes on the hydration of tricalcium silicateEnvironmental pollution is one of biggest challenges facing the world. The promising technology to control this problem is utilization of semiconductor materials as photocatalyst. It is well known that normal TiO 2 showing photocatalytic activity in the UV light, so to decrease the band gap and shifting into visible light, titanium dioxide nanotubes was doped with Fe 3+ ions. The influence of fabricated Fe‐doped TiO 2 nanotubes (Fe/TiNTs) on the hydration of tricalcium silicate (C 3 S) have been studied. Addition of 1.0 wt%, 2.0 wt% and 3.0 wt% of Fe/TiNTs into C 3 S system significantly accelerated the course of hydration. Study on the hydration products after 8h, 1d and 7d improved the degree of hydration. The enhancing of compressive strength of hydrated C 3 S after 7d, 14d and 28d was observed comparing to the normal TiO 2 nanotubes (TiNTs). Also treating both Fe/TiNTs and TiNTs with supersaturated Ca(OH) 2 solution revealed a strong interaction between Ca 2+ ‐ ions and nanotubes particularly in the presence of iron (Fe/TiNTs). The specific surface area of hydration products in the presence of Fe/TiNTs was increased. In this study, isothermal calorimetry was utilized for the course of hydration, x‐ ray powder diffraction (XRD) for the phase composition in combination with simultaneous thermal analysis (STA) and gas adsorption (GA) for measuring specific surface area of nanotubes and hydration products.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Synthesis and Characterization of Iron-Doped TiO2 Nanotubes (Fe/TiNTs) with Photocatalytic ActivityOne of the most significant global challenges for humans is environmental pollution. The technology to control this problem is the utilization of semiconductors as photocatalysts. In the current study, iron-doped titania nanotubes (Fe/TiNTs) with increased photocatalytic effect were synthesized via a modified hydrothermal method. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), gas adsorption, electron spin resonance (ESR) and UV–Vis diffuse reflectance spectroscopy (DRS). TEM results indicated that Fe/TiNTs have a tubular and uniform structure with an average outer diameter of 23–48 nm and length of 10–15 µm. ESR and DRS revealed that Fe3+ ions were successfully introduced into the TiNT structure by replacing Ti4+ ions. An enhanced light absorption in the range of 400–600 nm additionally indicated successful doping. The band gap was narrowed as iron wt% was increased. The photocatalytic activity was evaluated by the degradation of methyl orange (MO) in the presence of Fe/TiNTs and TiTNs by monitoring the degradation of MO under UV light irradiation. An acceleration on the hydration of Portland cement was observed in the presence of 2.0 wt% Fe/TiNTs. Fe/TiNTs can be used as a nanomaterial in cement-based building materials to provide self-cleaning properties to the surface of concrete even in indoor environments.Source Type:Article7 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , The facilitated synthesis of core‐multi‐shell silica nanopArticles and its performance onto cementitious based system in comparison with commercial silica nanopArticlesThe implementation of nanopArticles in cementitious systems have been studied for long time, however the knowledge about the influence of nanosized part (e.g. silica nanopArticles) has still to be fulfilled. The enhancement of cementitious matrix, specifically in the ultra‐high‐performance‐concrete (UHPC) system, has always been focused by researchers in various means of investigation and the application of silica nanopArticle plays a significant role as one of the attempts. Different methods have been applied for synthesizing silica nanopArticles (including the core multi‐shell silica nanopArticle) within this study to simplify the process. Moreover, the comparison of two types of silica nanopArticle (synthesized and commercial) has been done in mean of character and effect to the cementitious systems by appropriate methods, to be named as: size distributions examination, microscopic methods, investigation of mechanical properties, phases composition, etc. In order to hamper crack propagation at the nanoscale, a brand‐new and simple synthesized core multi‐shell silica nanopArticle with a high specific surface area was able for the first time be applied to the scope of cementitious matrices with an impressive impact on the properties of the investigated UHPC systems. This silica nanopArticle performs double functions: as nanoscopic shock absorber and as an additive to achieve a homogeneous nanoscale elastomer distribution and thus generates positive influence not only on the properties of UHPC, but also on future solutions for materials and environmental issues. With deep and meticulous study in the future, this type of complex nanopArticle is promising great applications to give a hand to find the solution for raw materials and therefore being closer to the aim of greener construction industry.Source Type:Article4